Support NLST for directory listing retrieval
Support NLST for directory listing retrieval

Currently, CoreFtp uses MLSD for directory listing retrieval. Unfortunately,
not all FTP servers support this command. This patch adds an alternative.
If the MLSD command ends with a command-not-implemented-error (or syntax
error), it tries to use NLST instead. However, NLST is less capable than
MLSD, so this does not really fit into the interface split between
ListFilesAsync and ListDirectoriesAsync, returning detailed
FtpNodeInformation, etc. Also, a better implementation would be more
general, allowing to use still other ways how to list files in FTP, and
detecting the correct command once at the connection open, e.g. using the
FEAT command. So, this is not a perfect final solution, I guess.

Fixes sparkeh9/CoreFTP#2

sparkeh9/CoreFTP